Darton Engine Sleeves - Block Party

How To Get Big-Block Displacement In A Small-Block Package

The Reader's Digest version is that the iron GM sleeves are cut out of the block and replaced with stronger sleeves capable of being bored out to sizes that are impossible with the factory offerings. The three ingredients for this are a donor block, a set of Darton MID sleeves, and someone with the skill to meld them together. Two-thirds of our recipe was handled leaving us needing to source a block. The good news is that since it was going to be heavily machined, we didn't need a new one. In fact, used is better since it's cheaper, and that helps offset the cost of the sleeves and labor. We found an old LS2 block with scored cylinders, but according to Steve, various LS blocks would be suitable candidates. As he explained, "I like the LS1 block because it has solid main webs with no cast-in breather holes. I will install the large bore, 4.200-inch sleeves, in the LS1 blocks but not the LS6. The LS6 blocks have the cast-in breather holes, making them too weak in my opinion, to bore out for the larger bore sleeves. Now, the Gen IV blocks also have breather holes, but on these blocks the floor of the coolant section has been raised leaving more material for the sleeves to sit on with much less chance of cracks developing than on the LS6 block. My preference in order on the Gen IV blocks is LS2, LS7, and then the L92/LS3/LSA/LS9 blocks, which are all the same in terms of sleeving. The LS7 sleeves are not cast into the block but pressed in at the factory, so they machine out, leaving sufficient parent aluminum to machine for the liners. The remaining blocks have cast-in liners with a larger outside diameter than on the LS2 blocks, which in itself isn't a problem. The problem is the lousy placement of the sleeves at the factory when the blocks are cast. Sleeves are not at 4.400-inch centers, or are shifted slightly to the front or rear or side to side, in the block, which gives me headaches during machining. I usually end up juggling the bores slightly away from the crank centerline axis to get the old sleeve completely machined out to the parent aluminum of the casting. This is especially important with MID where I need a nice smooth surface for the O-rings to seal against, or else coolant will leak into the crank case."

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The process of installing sleeves is an exercise in uber-tight tolerances. Bore centers must be held to within +/- .0005 inch. The bores themselves, for sleeve fitment, must be held to +/- .00025 inch, or a quarter of a thousandth of an inch! This is why having the right tools and skills are imperative. The CNC mill needs to be regularly qualified to make sure the backlash tolerances are within specification. Steve also opined on the importance of using a machine with flood coolant since the heat associated with the machining can screw up a block beyond repair. According to Steve, "Our shop is air conditioned, which I use in the summer to keep the temperature constant when machining. Otherwise, that twenty or so degree rise in temp from morning to afternoon will cause the block to expand in length and height. I've had blocks in here from shops doing the installs dry that were six-thousandths out of spec. In these cases the block can't be saved and the only option is to pull the sleeves and install them in a correctly machined block. I have done this for close to a dozen folks over the past few years. These shops did a pretty good job of screwing up the MID name when we first came out with the design for the LS blocks. I gave up my time fixing these screw ups for free to show people that when the work is done correctly there are very few issues with the MID blocks."

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If all of this sounds labor intensive, that's because it is. The basic charge to machine, stress relieve, install the sleeves, and deck the block is $1,175. Add in $100 to bore the block to within honing range and another $75 if you want the notches cut for rod clearance. The sleeves retail right around $1,300, so if you add it all up, you're at $2,650 for parts and labor. Well, plus a block. But good used donors can be found for $400 give or take. That means the total for a big-bore aluminum small-block would be in the three-grand neighborhood. Not cheap but very competitive to the aftermarket LS blocks currently on the market and less than two-grand more than a comparatively small 4.065-inch bore stock LS3 block from GM.

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Darton Engine Sleeves - Block Party

This is how Darton receives the ductile iron sleeves from the foundry. At this point it can become any number of sleeves from LS applications, to sleeves for Pro Stock and Funny Car engines. The sleeve's job is to control wear, heat, provide a platform for lubricity, and contain the combustion process without distortion. Cast iron is typically very inexpensive, breaks in well, and is brittle. The opposite of ductile iron, which is more expensive, very strong, has high elongation (meaning flexibility without breaking), and high surface hardness. Ductile is composed of a nodular structure as opposed to cast iron, which has a more graphite-flake structure.

The ductile iron sleeve is then machined and phosphate coated to protect against rust and corrosion. At this point all of the LS sleeves are the same.

The result is this LS sleeve kit. While there are eight sleeves, there are actually three part numbers here. The four in the center, cylinder one and eight, and cylinders number two and seven.

The coated sleeves are placed into the CNC mill for all the detail cutting and drilling. The sleeves for LS1 engines (Gen III) come in two bore size ranges. The smaller set covers from 4.125 to 4.160 inches, while the lager goes from 4.170 to 4.200 inches. For the Gen IV blocks, there's just one part number that covers from 4.125 to 4.200 inches.

For this install, we found a used LS2 block that had a couple of gouged factory sleeves. We made sure that block didn't have any cracks or other damage. This one set us back $400, which is almost $1000 cheaper than new from GM. Used LS1 blocks can be found for even cheaper.

After changing cutting heads, Steve then removed the rest of the cylinder material. Even though a lot of material is removed, the new sleeves are thicker and an MID-sleeved block will end up about six pounds heavier than a stock LS block.

The block is then set up on the CNC for final machining for fitment of the sleeves. The sleeve diameters are measured for size with a micrometer then numbered and the block is machined per sleeve for correct fitment. The sleeves will vary slightly in diameter so one must measure the sleeves prior to doing the finish bore work in the block.

The first thing Steve Demirjian, of Race Engine Development, did after getting the block onto his mill was to plot all the distances. To say this is precision work is an understatement.

After this pass, we were left with aluminum bores. "On the smaller bore Gen III and Gen IV LS2 blocks, I cut a honing clearance bore slightly larger than 4.200 inches to just above the main webbing. That leaves sufficient clearance to enable honing of the blocks to 4.200 inches if desired, without crashing the honing stones into the block," remarked Steve.

As you can see, quite a bit of material is removed in this process. It's also easy to see how someone inexperienced with this process could end up junking a perfectly good block.

Time to start removing material. The first pass of the mill cuts out the GM iron cylinder liners. According to Steve, "All machining must be done on a flood coolant machine or else the heat buildup during machining will distort and expand the block. This will make the tolerances impossible to hold and put stress into the block so that it will distort even further when the engine is started."

With the rough cuts done, Steve then stress-relieved the block. "This is a critical step that most shops do not do, or know about, for that matter. No stress relief and the block will distort in service, leaving bores that are four to five thousandths out of round. The same is true (but to a lesser extent) with the dry-liner installs. In any event, I have a Formula 62 stress relief machine which relieves the block at its natural resonant frequency. As far as I am concerned, this is the best stress relief machine on the market and is used by thousands of high-tech companies including Boeing and GM. I leave the block on the machine for an hour to reduce internal stresses from machining to a minimum," said Steve.

And here's the reason why cylinder one has a specific sleeve. The sleeve is cut with an angular flat to prevent breakthrough into the timing cover area. The block is machined to the exact mirror image of that sleeve flat.

And here's the reason why cylinder one has a specific sleeve. The sleeve is cut with an angular flat to prevent breakthrough into the timing cover area. The block is machined to the exact mirror image of that sleeve flat.

For an extra 75 bucks, Steve can also notch the cylinders to clear the rod bolts. Considering how hard the ductile iron is, we were more than happy to have him knock out the notches.

With the machining done, the block was deburred, washed, and blown dry. Before dropping in the sleeves, Steve gave the lower cylinders a light coat of Molykote O-ring lubricant. The tolerances are tight, and this helps the sleeves slide into place without damage.

We then used a dead blow mallet to carefully seat the sleeves into the block. Steve also gave us some advice on eventually installing the heads. He stated, "If using other than factory torque-to-yield head fasteners, the fasteners must be retorqued after the first heat-up/cool-down cycle prior to dyno runs. Failure to do this will most certainly result in a blown head gasket. Retorque requires backing off one fastener in the correct sequence then bringing back to torque. Then the next in sequence, and so on, until all are done on both banks." Also keep in mind that a MID-specific Cometic head gaskets must be used and are available from Darton.

After the three small O-rings were put in place, the sleeve was treated to some Molykote O-ring lube. The O-rings are there to keep coolant from leaking into the crankcase, which is exactly the same method used in wet-sleeve diesel engines.

The next day, Steve stress relieved the block for another half hour before beginning to deck the block. The final deck height ended up coming in at 9.235 inches.

Steve then applied a thin layer of Loctite 515 flange sealant (PN 51531) to the top of the sleeves. This is applied between the sleeves near the deck surface and around the flanges to both prevent leaks and hold the sleeves in place during decking and boring.

The sleeves were then secured in place and allowed to set-up overnight. It's important to keep in mind that the Loctite is there just to seal, and not hold the sleeves in place; that's eventually done by the heads being bolted on. Sleeved blocks (wet or dry) must never be washed in a jet wash without honing plates attached or the sleeves will be lifted out of position due to block expansion and will not reseat themselves. This is true even for aftermarket aluminum blocks. The preferred cleaning method is hand washing prior to assembly with warm soap and water.

Steve was also able to dowel our main caps using this slick jig. He charges $250 for the process, but it's money well spent since it adds stability to the rotating assembly. With this done, we were ready to finish-hone and align-hone the block.

We were then able to bore the block to within honing range. With this sleeve kit, we could have gone as large as 4.200 inches for the finished bore but went for a final bore of 4.185 inches. Combine that bore with a 4.125-inch stroker crank and the result would be an all-aluminum 454 small-block.

With that done, the sleeves could then be slid into the machined block. The sleeves are much stronger than the original block bores. This increase in strength allows the engine to make a lot more power without fear of cracking a cylinder wall. The sleeves are made of exactly the same material as what's used in Darton's Top Fuel and Funny Car sleeves.

Steve was also able to dowel our main caps using this slick jig. He charges $250 for the process, but it's money well spent since it adds stability to the rotating assembly. With this done, we were ready to finish-hone and align-hone the block.

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